Articles

Process mechanisms in ilmenite smelting (PDF)

Journal of the SAIMM

J.H. Zietsman and P.C. Pistorius

April 2005, vol. 105, no. 4, pp. 229

Extract:

Synopsis

It has previously been observed that industrial high-titania slags display a compositional invariance, remaining close to stoichiometric M3O5. The present study focuses on this invariance and the phenomena which may cause it. The invariance was studied using thermochemical calculations and a mechanism is proposed for the observed behaviour. The mechanism suggests that a combination of thermochemical equilibrium and transient slag solidification and melting results in the observed compositional invariance. The proposed mechanism provides new insights and prompts questions about other mechanisms in the smelting process.

Modelling of an ilmenite-smelting DC arc furnace process (PDF)

Minerals Engineering

J.H. Zietsman

Synopsis

Ilmenite smelters must be operated with the slag bath contained in a freeze lining of solidified slag to prevent refractory damage and ensure feasible furnace life. This makes the process an interesting and challenging one to operate and control.
The study focused on interactions between the freeze lining and slag bath. A mathematical model was developed to describe heat transfer, solidification and melting in the freeze lining and furnace wall. This model was incorporated into another model to yield a dynamic simulation-type model of the entire smelting furnace process. Simulation experiments with the models aimed to study the dynamic response of the freeze lining to changes in power input, slag composition, and operating parameters.
Due to confidentiality considerations, it was not possible to incorporate industrial data for comparison into the study. Regardless of this, the results still remain useful to practitioners when considering the process aspects that were investigated.

Calculation of FeO-TiO2-Ti2O3 liquidus isotherms pertaining to high titania slags (PDF)

Journal of the SAIMM

D.J. Fourie; J.J. Eksteeen and J.H. Zietsman

November 2005, vol. 105, no. 5, pp. 695

Extract:

Synopsis

During the production of pure TiO2 for the pigment industry, ilmenite, containing 35-60% TiO2, is reduced to high titania slag, containing 70-95% 'TiO2' pig iron. The high titania slag produced, consists mainly of titanium in different oxidation sates and FeO in equilibrium with liquid iron. To predict the phase and chemical reaction equilibruim in a furnace, a suitable solution model is required with accurately determined binary interaction parameters, as slag metals tend to behave very non-ideally. This paper investigates two popular slagmodels, namely modified quasi-Chemical (MQC) model and the cell model and provides the binary interaction parameters based on recently published data of the ternary system and critically assessed published urnary and binary data. Very few modelling results have been published on the ternary Ti-Fe-O system pertaining to high titanium slags. The solutions models, with their regressed interaction parameters, can subsequently be implemented in commercial software of the slagmetals phase equilibrium to predict how much and which type of solids will precipitate for a given bulk slag chemistry and operating temperature or, alternatively, above which temperature should a furnace be operated to avoid excessive solid precipitation.

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